O. A. Krishtal

P2X receptors and synaptic plasticity

Adenosine triphosphate (ATP) is released in many synapses in the CNS either together with other neurotransmitters, such as glutamate and GABA, or on its own. Postsynaptic action of ATP is mediated through metabotropic P2Y and ionotropic P2X receptors abundantly expressed in neural cells. Activation of P2X receptors induces fast excitatory postsynaptic currents in synapses located in various brain regions, including medial habenula, hippocampus and cortex. P2X receptors display relatively high Ca2+ permeability and can mediate substantial Ca2+ influx at resting membrane potential. P2X receptors can dynamically interact with other neurotransmitter receptors, including N-methyl-D-aspartate (NMDA) receptors, GABA(A) receptors and nicotinic acetylcholine (ACh) receptors. Activation of P2X receptors has multiple modulatory effects on synaptic plasticity, either inhibiting or facilitating the long-term changes of synaptic strength depending on physiological context. At the same time precise mechanisms of P2X-dependent regulation of synaptic plasticity remain elusive. Further understanding of the role of P2X receptors in regulation of synaptic transmission in the CNS requires dissection of P2X-mediated effects on pre-synaptic terminals, postsynaptic membrane and glial cells.

From Galvani to patch clamp: the development of electrophysiology

The development of electrophysiology is traced from the early beginnings represented by the work of the Dutch microscopist, Jan Swammerdam, in the 17th century through the first notion of an aqueous transmembrane pore as a substrate of excitability made by Luigi Galvani in late 18th century to the invention late in the 20th century of the patch-clamp technique by Erwin Neher and Bert Sakmann.

P2X3 receptor gating near normal body temperature.

P2X3 purinoreceptors expressed in mammalian sensory neurons are involved in nociception, mechanosensory transduction, and temperature sensation. Homomeric P2X3 receptors desensitize rapidly (<500xa0ms after activation by an agonist) and recover from desensitization very slowly (20–25xa0min at room temperature). They are susceptible to use-dependent inhibition by low nanomolar concentrations of ATP through developing the “high-affinity binding site” (HABS), which traps ATP molecules, thus keeping receptors in a desensitized state (Pratt et al., J Neurosci 25:7359–7365, 2005). Indeed, here we demonstrated directly that the desensitization of the receptor, after being activated by ATP, proceeds independently of the presence of agonist. We found that the temperature sensitivity of P2X3 receptors is abnormal: development of desensitization does not depend on temperature within the range between 25 and 40°C, whereas the recovery from desensitization is greatly accelerated with temperature increase (Q10 ∼10). The sensitivity of HABS to low nanomolar ATP near normal body temperature (35°C) is substantially lower than at 25°C (IC50 is 3.2u2009±u20090.3xa0nM at 35°C and 0.79u2009±u20090.09xa0nM at 25°C). HABS itself is subjected to slow desensitization partially loosing its sensitivity to ATP: at 35°C the response completely recovers in 10xa0min in the presence of 3xa0nM ATP, making the receptor operational in the presence of up to 30xa0nM ATP. Unusual combination of temperature sensitivity/insensitivity of P2X3 receptors may be related to their pivotal role in the processing of thermal sensitivity as revealed by recent knockout experiments.

Novel mechanism for temperature-independent transitions in flexible molecules: role of thermodynamic fluctuations.

A novel physical mechanism is proposed to explain the temperature-independent transition reactions in molecular systems. The mechanism becomes effective in the case of conformation transitions between quasi-isoenergetic molecular states. It is shown that at room temperatures, stochastic broadening of molecular energy levels predominates the energy of low-frequency vibrations accompanying the transition. This leads to a cancellation of temperature dependence in the stochastically averaged rate constants. As an example, a physical interpretation of temperature-independent onset of P2X{3} receptor desensitization in neuronal membranes is provided.

Extracellular cAMP inhibits P2X3 receptors in rat sensory neurones through G protein-mediated mechanism

Aim:u2002 To identify the mechanisms of P2X3 receptor inhibition by extracellular cyclic adenosine monophosphate (cAMP) in rat dorsal root ganglion (DRG) neurones.

Adenosine Triphosphate (ATP) as a Neurotransmitter

Adenosine triphosphate (ATP) is an important extracellular signaling molecule. ATP acts as a neurotransmitter in both peripheral and central nervous systems. In the peripheral nervous system, ATP is involved in chemical transmission in sensory and autonomic ganglia. In the central nervous system, ATP, released from synaptic terminals, induces fast excitatory postsynaptic currents. Postsynaptic action of ATP is mediated by a plethora of ionotropic and metabotropic receptors. Furthermore, ATP also acts as an important mediator in neuronal–glial and glial–glial signaling. All types of glial cells are endowed with diverse ATP receptors, which trigger Ca2+ signaling events and membrane currents. ATP can also act as a ‘glio’transmitter released from astroglial cells via regulated exocytosis or through plasmalemmal channels.